1. Field of the Invention
Embodiments of the present invention generally relate to a construction equipment attachment for aligning a lead and hammer with an object to be driven. The invention is particularly suitable for driving objects such as a timber piles, steel piles, pipe piles, steel sheet piles, h-beam and the like, into the earth.
2. Description of the Related Art
Buildings, bridges and other structures often require pilings driven into the earth in order to either reach strata suitable for supporting the load of the structure or to a depth that the frictional force between the earth and the pile is sufficient to safely support the structure. For many larger structures, the pilings are driven through the soil to the underlying bedrock, which may lie a considerable distance below the earth's surface. To reach such depths, piles are driven utilizing heavy construction equipment that can deliver blows exceeding 7 tons per impact.
FIG. 1 depicts a simplified schematic drawing of a conventional pile driving system 100. The pile driving system 100 typically includes a lead 102 and a hammer 104 suspended by a crane 106. The hammer 104 is coupled to and is free to slide linearly along the lead 102. The lead 102 includes a stop at its lower end to prevent the hammer 104 from disengaging from the lead 102. The lead 102 is positioned by the crane 106 and the piling is hoisted into position alongside the lead 102. The hammer 104 is lowered by the crane 106 to engage the hammer 104 with the piling. During this operation, the lead 102 and piling are manually aligned to the planned position for driving.
The suspended lead 102 relies on gravity and one or more tethers 116 to maintain a vertical orientation and provides a guide for both the hammer 104 and the piling 108 to be driven into the ground 110. The hammer 104 is typically powered by air or hydraulics to provide reciprocating blows to the top of the piling 108 to force the piling into the ground 110. Although the lead 102 may be tethered at its lowered end by a cable or linkage 116 to the crane 106 to maintain the alignment of the lead 102 with the piling 108, it is difficult to maintain the hammer 104 and piling 108 on a coaxial orientation. If the hammer 104 is not maintained in a true coaxial orientation with the piling 108, the piling will be impacted at an angle relative to the centerline of the piling. Thus, the full force of each hammer blow will not be complete transmitted into a force directing the piling 108 into the ground 110.
The load bearing capability of the piling may be determined at the construction site by counting the number of hammer blows of a known force required to drive the piling a unit distance into the ground. Thus, if the piling and lead are misaligned and the full force of the hammer blow does not force the piling downward, the number of blows per unit distance that the piling is driven will erroneously indicate piling load bearing capacity as being greater than the true load bearing capacity of the piling. False load bearing information may result in unwanted settling of structures built on the pilings, or even catastrophic structural failure.
Another major challenge when using conventional suspended leads is the avoidance of overhead power lines and other overhead obstacles. Power lines at construction sites make it difficult to maneuver the crane and lead into operating position, and in some instances, must be removed to provide enough clearance for the crane to adequately support the lead or support the head over the planned pile position. Removal of these obstacles presents a major and expensive challenge to contractors charged with driving the pilings.
Therefore, there is a need for an improved pile driving device.